IRR Solver implementation

Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

Record owner

Guth Instruments

Lifecycle

verified-clean

Evidence ID

t6-021

Effect

Computation or source lookup only

Input and validation requirements

The specification exposes undefined evaluations at r=-1, no-real-solution cash flows, and multiple IRRs; a solver that assumes one finite root or does not guard the 1+r denominator can fail or return a misleading result.

Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

{
  "inputs": {
    "cash_flows": [
      -1000,
      1100
    ],
    "method": "Newton-Raphson",
    "initial_guess": 0,
    "tolerance": 1e-10,
    "period": "annual"
  },
  "expected_outputs": {
    "irr_decimal": "0.100000000000000",
    "irr_percent": "10.0000000000000%",
    "convergence": "converged"
  },
  "working": "NPV(r) = -1000 + 1100/(1+r). NPV'(r) = -1100/(1+r)^2. Iteration 0: r0=0, NPV=100, NPV'=-1100, so r1=0-100/(-1100)=0.0909090909. Iteration 1: NPV(r1)=-1000+1100/(12/11)=-1000+1008.333333=8.333333; NPV'(r1)=-1100(11/12)^2=-924.305556; r2=0.0909090909-8.333333/(-924.305556)=0.0999248685. Iteration 2 gives r3 approximately 0.0999999949, and the next iteration gives 0.100000000000000. Therefore IRR=10.0000000000000%."
}

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche6/tranche6-results.json